The light of a common fire-fly will enable a person to
distinguish the hour on a dial in a dark night, but the glow from
the grub described will render the smallest print so legible that
a page may be read with case. I once tried the experiment of
killing the grub, but the light was not extinguished with life,
and by opening the tail, I squeezed out a quantity of glutinous
fluid, which was so highly phosphorescent that it brilliantly
illumined the page of a book which I had been reading by its
light for a trial.
All phosphorescent substances require friction to produce their
full volume of light; this is exemplified at sea during a calm
tropical night, when the ocean sleeps in utter darkness and
quietude and not a ripple disturbs the broad surface of the
water. Then the prow of the advancing steamer cuts through the
dreary waste of darkness and awakens into fiery life the spray
which dashes from her sides. A broad stream of light illumines
the sea in her wake, and she appears to plough up fire in her
rush through the darkened water.
The simple friction of the moving mass agitates the millions of
luminous animalcules contained in the water; in the same manner a
fish darting through the sea is distinctly seen by the fiery
course which is created by his own velocity.
All luminous insects are provided with a certain amount of
phosphorescent fluid, which can be set in action at pleasure by
the agitation of a number of nerves and muscles situated in the
region of the fluid and especially adapted to that purpose. It
is a common belief that the light of the glow-worm is used as a
lamp of love to assist in nocturnal meetings, but there can be
little doubt that the insect makes use of its natural brilliancy
without any specific intention. It is as natural for the
fire-fly to glitter by night as for the colored butterfly to be
gaudy by day.
The variety of beautiful and interesting insects is so great in
Ceylon that an entomologist would consider it a temporary
elysium; neither would he have much trouble in collecting a host
of different species who will exhibit themselves without the
necessity of a laborious search. Thus, while he may be engaged
in pinning out some rare specimen, a thousand minute eye-flies
will be dancing so close to his eyeballs that seeing is out of
the question. These little creatures, which are no larger than
pin's heads, are among the greatest plagues in some parts of the
jungle; and what increases the annoyance is the knowledge of the
fact that they dance almost into your eyes out of sheer vanity.
